Will test whether modulation occurs at several sites in the human polymeric immunoglobulin-secretory component (PIg-SC) pathway. The effect of binding monovalent (PIg) and/or polyvalent (IgG-SC) ligands to membrane PIg receptor (PIgR) on the display and function of PIgR will be evaluated in epithelial cell lines at the protein and mRNA levels and in vivo in humans.